1. Field of the Invention
The present invention relates to a light-emitting diode, and a light-emitting device, a lighting apparatus, a display, and a signal light using the same.
2. Description of the Related Art
Light-emitting diodes have the advantages of energy conservation and long service life and have come to attract attention as a light source of a light-emitting device, a color image display device, a backlight of a liquid crystal panel, or a traffic light.
Taking a blue light-emitting diode as an example, the light-emitting diode has a structure that a buffer layer, an n-type GaN layer, an active layer, a p-type GaN layer, and a transparent electrode layer are sequentially deposited on a substrate made of sapphire, as disclosed in Japanese Unexamined Patent Application Publication No. 2001-210867, for example.
On the transparent electrode layer, partially, there is formed a p-side electrode, while the transparent electrode layer, the p-type GaN layer, and the active layer are partially dry-etched to partially expose the n-type GaN layer, providing a structure where an n-side electrodes is formed on the exposed n-type GaN layer. Similar multilayer structures and electrode structures are also disclosed in Japanese Unexamined Patent Application Publication Nos. 2009-71337 and 2008-153634.
In the conventional light-emitting diode, as described above, while the p-side electrode is formed on the transparent electrode layer that will serve as a light-emitting surface, the transparent electrode layer, the p-type GaN layer, and the active layer are partially dry-etched to partially expose the n-type GaN layer, providing a structure where the n-side electrode is formed on the exposed n-type GaN layer, so that the light-emitting area decreases by the area occupied by the p-side and n-side electrodes. As a matter of course, this also decreases the light emission amount, as well as the light emission efficiency.
In addition, since the structure is such that the n-side electrode is formed in a restricted and concentrated manner at the portion where the n-type GaN layer is exposed, the electric current tends to concentrate on this portion, preventing uniform surface light emission.
In order to perform dry-etching for formation of the n-side electrode, moreover, an ICP-RIE has to be used. The ICP-RIE, which is used for many purposes in Si micromachining (MEMS), as well as for high-frequency device processing using compound semiconductor etching or thin-film magnetic head processing using AlTiC etching, is extremely expensive. The great equipment cost is reflected in the increased cost of light-emitting diodes.